Research has linked the drugs with a number of side effects, such as muscle pain, increased blood sugar and memory problems. But the majority of patients have no side effects at all.

Days after running out of pills and forgetting to refill his prescription, McDonagh felt different. He was more aware of his peripheral vision and could change lanes on the freeway without feeling nervous.

"It was pretty dramatic," McDonagh told CNN.

So he decided to stop taking the medication altogether. Now a new study, published Monday, follows how patients like him fare after going off these drugs.

Researchers studied over 28,000 patients in Massachusetts and found three in 10 stopped taking statins after experiencing side effects, which were presumed to be due to the drugs. Some 8.5% of them had a cardiovascular event, such as a heart attack or stroke, within four years -- versus 7.6% of those who continued taking statins.

And 6.6% of patients who stopped taking statins died of all causes, versus 5.4% of those who kept taking them. The researchers did not have information on what the causes of death were.

Taken together, that's a 1.7% difference in these negative outcomes, the researchers noted.

"That's a very significant number," said Cleveland Clinic cardiologist Dr. Steven Nissen, who was not involved in the study but penned an accompanying editorial in the same journal. "Those kinds of numbers are typically what we see for very effective therapies."

In other words, 59 of these patients would need to continue taking statins for four years to prevent one case of heart attack, stroke or death, Nissen said.

Dr. Alexander Turchin, an author of the new study and an associate professor of medicine at Harvard Medical School, wasn't surprised by his findings. He said the research fell in line with what we already knew about the benefits of statins.

Turchin also receives grants from pharmaceutical companies, but those grants did not fund this new research.

One expert questioned whether his findings had much to do with statins at all.

"We don't know what (else) was different about the groups," said Dr. Rita Redberg, a professor of medicine at University of California, San Francisco. Redberg was not involved in Turchin's research. "People that take medicines and are adherent do better than people that don't."

For example, those who take medications consistently might also eat better or exercise more, Redberg added. So a "small difference" between the groups "isn't that revealing," she said.

Redberg also noted that the study did not separate patients who had already had a heart attack or stroke. She said that there is plenty of good evidence to recommend statins to patients who have had cardiovascular problems, but that there is "little to no benefit" in using statins to prevent a cardiac event in those who haven't had one before. The latter remains a topic of debate.

Experts say that McDonagh's experience as a patient is uncommon, but exactly how uncommon is unclear. It is difficult to know whether a reported symptom is truly caused by statins, and many studies do not ask patients about common side effects, according to experts.

Roughly one in five patients on statins experienced a side effect, the new study found. This is higher than other studies have estimated, but it could have to do with the way the study was designed, Turchin said.

Nissen said that statins have developed a "bad reputation with the public," largely due to websites that peddle scary and unscientific claims about statins.

"We have a large number of people in the public that have been convinced by this internet cult that statins are bad for you," said Nissen, who compared the trend to discussions surrounding vaccines and climate change. "How did we get into this kind of a mess?"

Success! An email has been sent to with a link to confirm list signup.

Error! There was an error processing your request.

WEEKLY HEADLINES

Get breaking news and latest headlines delivered to your inbox every Sunday and Wednesday. Plus, From the Newsroom: A behind-the-scenes look at how we make decisions, what's coming up and more.

These claims, Nissen said, could actually increase reported side effects. The more patients are aware -- and perhaps fearful -- of statins and their side effects, the more likely they are to report those side effects. This phenomenon is known as the "nocebo effect," the opposite of the placebo effect.

Heavy media coverage of statins may also lead people to stop taking them, according to a study from the UK. However, this effect disappeared after six months.

"It's our human nature that we are interested in negative news much more than we're interested in positive news," said study author Turchin, also a practicing endocrinologist at Brigham and Women's Hospital.

McDonagh is no stranger to confusion over these medications. When he finally connected the dots between his medications and his symptoms, he found other people talking about the same thing online. He said patients may get mixed messages from optimistic doctors, the skeptical internet and even drug commercials, whose fast-talking voiceovers list off side effects.

"You've got a very short period of time with the doctors," he told CNN. "The onus is sometimes on the patients to check these things."

When patients come to Turchin with side effects, he said they weigh the risks for heart attack and stroke, the severity of their symptoms and how likely it is that those symptoms are due to the statin itself. Some patients may try a different statin.

Of the patients who continued taking statins in the new study, nearly two in five changed to a different statin. About a quarter of them reported a side effect on the new statin.

Realizing that statins wouldn't work for him, McDonagh found the motivation he needed to lose weight. He lost roughly 45 pounds and has kept most of it off. While he acknowledged that statins can be a big benefit to some, he stands by his decision.

"I've got no regrets right now," said McDonagh. "I haven't had a heart attack."